You’re describing 464XLAT, it’s how T-Mobile internet works. iOS, macOS and windows all support what you describe out of the box (although last I checked, Windo

You’re describing 464XLAT, it’s how T-Mobile internet works. iOS, macOS and windows all support what you describe out of the box (although last I checked, Windows inexplicably only does this if the interface is a mobile/5G interface. They may have fixed this.) You can try this on a vanilla macOS install if the router advertisement hints at a NAT64 prefix (RFC8781) and you either don’t run DHCP4, or your DHCP4 server lists the IPv6-preferred option (RFC8925). I think they’ve also added a check to query a well-known ipv4-only hostname on DNS, and if it gets a AAAA back and the connection works, it knows it must be behind a working nat64 setup, which obviates the need for the router advertisement to have the PREF64 option. I tried this a year ago and it worked great, macOS skips DHCPv4 and gives itself a single 192.0.0.1/32 address so that legacy apps can “see” an IPv4 interface, and any packets sent from it are translated to IPv6 and sent to the nat64 prefix. So “ping 1.1.1.1” works fine. I stopped using this though, because I have a garage door opener (ratGDO) that only works with ipv4, and my nat64 prefix can’t “hair-pin” the packet back to the LAN address… it basically only works if everything on your LAN is IPv6, which my garage door is not. I think android supports this as well, but I’m not sure about vanilla Linux, I think you need to install a clat daemon to do the translation. It did take way too long for this to work though, as you point out.